The Kester 5520 cleaner is a non-fuming liquid solution for removing oxides, sulfides, carbonates and other contamination, such as etch residues, from copper metal surfaces to facilitate soldering. This stable solution cleans by dissolving or solubilizing the contamination for easy removal by water rinsing. The chemical cleaning action is quite different form strong mineral acids which etch away valuable base metal and passivate the surface by insoluble film formation. - 5520 contains a pink pH indicator which turns yellow at pH 3.5 indicating the solution has lost its efficiency. Because the etch rate is controlled, the bath life is very extended. 5520 will selectively remove surface contamination from copper or gold-plated surfaces with no appreciable metallic etching.